1. Field of the Invention
The present invention relates to a sound insulation structure including a cover member for reducing radiant sound generated from a power unit for generating motive power, and a resonator for reducing the radiant sound. More particularly, the present invention relates to the layout of the resonator in relation to the power unit and the cover member.
2. Background of the Invention
An internal combustion engine as a power unit is know to have a cover member attached thereto for reducing radiant sound generated from an internal combustion engine. A resonator is formed inside the cover member integrally with the cover member so as to reduce the noise in a space defined by the internal combustion engine and the cover member. In addition, a neck part of the resonator is opened into the space (refer to, for example, Japanese Patent Laid-open No. Hei 8-144783).
In addition, a system is known wherein a power unit includes an internal combustion engine and a transmission supplied with motive power of the internal combustion engine and in which the transmission is composed of a swash plate type hydrostatic continuously variable transmission (refer to, for example, Japanese Patent Laid-open No. 2005-248838 and Japanese Patent Laid-open No. 2005-263143).